are the pictures pornographic? While there are plenty of sites that are specifically designed for just such a purpose, there are a lot more webspace providers/hosts that would consider it a violation of their rules.

has she consented? Even it is legal to post her photos without her knowledge, it's certainly not a considerate thing to do and maybe not be the wisest either.

are the photos copyright protected? If they were taken by a professional photographer, you can't legally post the photos without the photographers permission. However, if you took the pix yourself you own the copyright. The safest things to do in ''all'' of these cases would be to get her permission (written would be ideal, just in case the two of you break up) and to read your host's TOS

And finally, this is more important than anything else...

Is she a minor? If she is, it would be safest not to post them at all. If she's a minor and the pictures are overtly sexual in nature or even just sexually suggestive...forget it. Child pornography is a very serious crime.

I would suggest you visit a website where you can ask for legal advice like freeadvice.com or www.worldlawdirect.com/asklawyer

If you are still uncertain about legality, err on the side of caution and don't do it.